Production of thermoplastic polymeric material



Patented Apr. 27, 1948 PRODUCTION OF THERMOPLASTIC POLYMERIC MATERIAL Henry Dreyfus, London, England; Claude Bonard, administrator of said Henry Dreyfus, deceased. assignor to Ceianeae Corporation of America, a corporation of Delaware No Drawing. Application August 2, 1944, Serial No. 547,805. In Great Britain July 26, 1943 1 Claim.- (Cl. 260-83) l 2 This invention relates to thermoplastic polytemperature even before any evaporation has ocmeric material and in particular to material of curred. During evaporation, owing to preferenthe kind specified having a basis of a polymerised tial loss of the volatile liquid, the solvent power olefinic compound and a plasticiser therefor, and of the liquid medium is progressively still furto the production of such material. 5 ther reduced. The solvent power of the liquid Polymeric material of the kind referred to medium may, on the other hand, be so low iniabove, for example compositions comprising polytially that some separation of polymeric matemethylmethacrylate or other polymerised monorial occurs even at the temperature of polymermer having a basis of acrylic acid or a derivative isation; or the solvent power may be suillciently thereof, together with a plasticiser, are largely high ior the polymeric material to remain in soluused as moulding stock for the production of tion even when the reaction mixture is cooled to articles by injection moulding, or compression ordinary temperature, precipitation occurring as moulding at an elevated temperature. For this the liquid medium is evaporated.

purpose such polymeric material is commonly It is of advantage to work with highly concenemployed in powder form. The present invenl5 trated solutions, 1. e., solutions in which the tion provides a simple method of obtaining the monomer is dissolved in less than its own weight polymeric material in the form of a powder or of the liquid medium. The best results have been of a friable mass that can easily be reduced to a obtained under the iollowing conditions: in the powder. initial reaction mixture the weight of the liquid According to the present invention the D IY- medium (water plus volatile liquid) is between merisation is brought about while the oleflnic about 50% and about 100% of the weight of the substance is in solution in a homogeneous liquid monomer; this reaction mixture forms two liquid medium comprising water and a water-soluble phases at ordinary temperature but becomes hovolatile liquid which is a solvent for the polymer, mogeneous at the temperature at which polymersaid liquid medium being such that on evaporaisation is carried out; at the end of the polytion it progressively loses solvent power for the merisation process the reaction mixture consists polymeric material, and the polymeric material of a large body 01 viscous liquid containing the is obtained in granular or friable form by evapbulk of the polymeric material together with a crating said medium from the reaction mixture very much smaller body of supernatant liquid; after polymerisation. It is frequently of advanand during cooling oi this large body of liquid tage for the polymeric material to contain a plasto ordinary temperature precipitation of the polyticiser for the polymer. Such plasticised material meric material (polymer plus plasticiser) occurs.

can be obtained according to the invention by The invention may be illustrated in connection dissolving a suitable plasticiser in the liquid with the production of a moulding powder commedium. prising polymethyl methacrylate plasticised with Preferably the olefinic substance is an aliphatic dimethyl phthalate. For this purpose a reaction ester containing a single olefinic group, the polymixture of the following composition may be merisation is carried out in a closed vessel at made, the parts being by weight: super-atmospheric temperature and using an or- Parts ganic peroxide as catalyst, and the volatile liquid Methyl methacrylate 125 is a compound of carbon, hydrogen and oxygen Dimethyl phthalate 10 which does not contain a hydroxyl group and is Acetone 64- stable in the presence'oi the peroxide. Water 23.5 The solvent power of the liquid medium for the Benzoyl permridp 3 3 polymeric material (1. e., for the polymer plus plasticiser or for the polymer alone when no plas- The reaction mixture may be made by mixing the ticiser is employed) may be varied by varying monomer, plasticiser and acetone, adding the catthe proportion of water in the liquid medium. alyst, filtering the solution and introducing the The best results have been obtained when the specified proportion of water. In the cold this proportion of water in the liquid medium is suiilo reaction mixture forms two liquid phases but on ciently high (and the solvent power in conseheating, the solution becomes homogeneous. quence sufliciently low) for precipitation of the Polymerisation may be carried out at about 100 polymeric material to occur when the reaction C. and it is preferred to continue the reaction for mixture is cooled from the temperature at which about 16 hours so as to ensure substantially compolymerisation has been carried out, to ordinary plete polymerisation or the monomer. The acetone is then rapidly removed from the reaction mixture by vaporisation, preferably under reduced pressure, with irothing, leaving a friable mass which can easily be crumbled into a powder with the desiredflneness without any substantial expenditure of power. This powder is then dried free from water and is ready for use.

It will be observed that this process enables the moulding powder to be produced without a power-consuming grinding operation such as is necessary when moulding powders are formed from the tough, solid masses of plasticised polymer obtained by incorporating the plasticiser with the aid of solvents; the complications of the emulsion method of polymerisation are avoided; separation of the moulding powder from the liquid medium in which the reaction is carried out is very simple and does not involve the use of any liquid which might remove a part of the plasticiser as do, for example, processes in which the plasticised polymer is precipitated from solution in a liquid parafiln medium which must subsequently be removed from the powder by washing with a more volatile liquid hydrocarbon. Seasoning of articles moulded from the moulding stock of the invention is not in general necessary since substantially the whole of the volatile solvent is readily removed from the powder by vaporisation.

It is not essential to employ the various constituents in the proportions specified; thus for example the proportions of water to acetone can be varied so long as the resulting mixture remains a solvent for the monomer, plasticiser and catalyst at the temperature of polymerisation and either a non-solvent for the plasticised polymer at ordinary temperatures or a solvent therefor which becomes a non-solvent on losing a proportion of the acetone.

Instead of acetone, we may employ other volatile solvents for the polymer which are miscible with water and are compounds of carbon, hydrogen and oxygen which do not contain hydroxyl groups and are stable in the presence of the catalyst employed. 'The volatile solvent may, for example, be an ester such as methyl acetate, or an ether such as methylal or methylene ethylene ether, or an aliphatic ketone such as methyl ethyl ketone.

Other plasticisers can be employed instead of dimethylphthalate, e. g., diethyl phthalate, dibutyl phthalate, di- (methoxyethyl) 'phthalate, methyl-phthallyl ethyl glycollate, tricresyl phosphate and tri- (monochlorethyl) phosphate. Plasticisers which are soluble to a substantial degree in water, are of course, unsuitable.

The invention has been described with particular reference to the use of methyl methacrylate as the monomer. We may, however, employ other olefinic substances which are capable of forming solid polymers. Among such oleflnic compounds are ethyl acrylate and other esters of acrylic acid may be effected according to the process oi the invention.

In conducting the polymerisation, other catalysts than benzoyl peroxide may be employed. For example, otherorganic peroxides and peracids, for example peracetic acid may be used; or polymerisation may be effected without a catalyst, for example by irradiation'with ultra-violet light.

The principle of obtaining polymers of the kind referred to in the form of a powder or'oi a friable material which can easily be reduced to a powder, by removal of a volatile solvent for the polymer, by vaporisation from a solution of that polymer, with or without a plasticiser therefor, in a homogeneous mixture of the volatile solvent and water, is believed to be broadly novel.

Having described my invention, what I desire to secure by Letters Patent is:

Process for the solution polymerization of methyl methacrylate, which comprises efiecting said polymerization in a reaction medium comprising aqueous acetone, containing a plasticizer for the polymer, in an amount equal to 50 to 100% of the weight of the monomer, the ratio of acetone to water being about 8:3 the polymerization being carried out in a closed vessel at about 100 C. in the presence of a peroxide polymerization catalyst 'in solution, until substantially all the monomer is converted to polymer,

all the polymer formed remaining in solution at the polymerization temperature although the reaction medium is not capable of holding the polymer in solution at atmospheric temperature, and

then recovering the polymer in friable form by the evaporation of the acetone.

HENRY DREYFUS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,072,904 ,Ries Mar. 9. 1937 2,121,839 Strain June 28, 1938 2,129,662 Barrett et al Sept. 13, 1938 2,135,443 Strain Nov. 1, 1938 2,205,883 Graves June 25, 1940 FOREIGN PATENTS Number Country Date 482,701 Great Britain Apr. 4, 1938 

